The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Sharking off Ocean Beach San Francisco

About three weeks ago here in San Francisco, the weather was unusually warm. So it was a great time to hunt for superior mirages. I decided to go to Ocean Beach (near San Francisco) to look for superior mirages. At the horizon I really saw a superior mirage of Point Reyes, but something that was much closer suddenly caught my attention. There were two gray whales swimming very close to shore. As a matter of fact, they were so close that a man on a surf board got right next to them. Suddenly, I saw something else in the ocean. I was looking against the low Sun and, at first, I thought that one of the whales had poked its head out of the water, but I wasn't sure. When I got home, and looked at the image on my computer, I saw that the head was not the head at all. It looked like a fin - a shark fin! I’ve read that gray whale mothers and babies swim close to shore to avoid being attacked by sharks and orcas. Everything was adding up, a huge shark patrols Ocean Beach, in the vicinity of surfers. I alerted the authorities about this sighting and then sent my photo to several shark experts. Most of them agreed it was the fin of the great white shark. One of them wrote, "It looks like it is likely a white shark - one that we know quite well in fact. The image is a bit tough to make a sure ID but it looks like it could be a shark we know as sicklefin - from his distinct damage on the dorsal fin." Another expert thought it was a basking shark since these sharks had been recently sighted off Morro Bay.

However, Bill Keener from the Golden Gate Cetacean Center wrote to say, “Your mystery photograph shows only part of a gray whale, one of its flukes (half of the tail), because this is what you see sometimes when the whale is feeding." Unlike most other whales, grays are often bottom feeders. They'll even roll on their side to get their mouth as close to the bottom as possible, sucking up mud filled with worms and crustaceans. As gray whales migrate to Alaska along the California coast, there's generally very little feeding activity. Therefore, not many people see these fluke displays. The adult whale simply rolled onto one side and all that was sticking up in the air was the top half of a tail fluke. Because the end of the fluke looks like a huge shark fin, sometimes this behavior is called sharking. In the end, I took a photo not of a shark but of sharking.